1. Field
The present invention generally relates to an ultrasound system, and more particularly to a method of displaying an elastic image in the ultrasound system.
2. Background
An ultrasound system has become an important and popular diagnostic tool since it has a wide range of applications. Specifically, due to its non-invasive and non-destructive nature, the ultrasound system has been extensively used in the medical profession. Modern high-performance ultrasound systems and techniques are commonly used to produce two or three-dimensional images of internal features of an object (e.g., human organs).
The ultrasound system generally uses a probe containing a wide bandwidth transducer to transmit and receive ultrasound signals. The ultrasound system forms images of human internal tissues by electrically exciting an acoustic transducer element or an array of acoustic transducer elements to generate ultrasound signals that travel into the body. The ultrasound signals produce ultrasound echo signals since they are reflected from body tissues, which appear as discontinuities to the propagating ultrasound signals. Various ultrasound echo signals return to the transducer element and are converted into electrical signals, which are amplified and processed to produce ultrasound data for an image of the tissues.
Generally, the ultrasound image is displayed in a Brightness-mode (B-mode) by using reflectivity caused by an acoustic impedance difference between the tissues of the target object. However, if the reflectivity of the target object is hardly different from those of the neighboring tissues such as tumor, cancer or the like, then it is not easy to recognize the target object in the B-mode image. Further, an ultrasound elastic imaging technology has been developed to display an image of the target object by using mechanical characteristics of the target object. Such technology is very helpful for diagnosing lesions such as cancers. The tumor or cancer is relatively stiffer than the neighboring tissues. Thus, when stress is uniformly applied, a variation of the tumor or cancer is typically smaller than those of the neighboring tissues.
An elasticity of a tissue is measured by using ultrasound data obtained before and after compressing the tissue. A compression plate mounted on an ultrasound probe is used to compress the tissue. A user may press the compression plate on the target object, thereby compressing the tissues of the target object. In such a case, strain in the tissues depends on the pressure applied by the user. The quality of an elastic image may be changed according to the pressure applied to the tissue. For example, if the pressure is relatively weak, then a difference in strain between the tumor or cancer tissue and the neighboring tissues thereof tends to be very small, while the tumor or cancer is hardly distinguishable from the neighboring tissues in the elastic image.
Further, if the pressure is relatively hard, then a correlation between the tumor or cancer tissue and the neighboring tissues becomes lowered. This is so that the quality of the elastic image can be deteriorated. Therefore, an appropriate pressure is required to obtain an enhanced elastic image. Experimentally, when the strain of the tissues falls within a range of 0.5-3%, an optimal elastic image can be obtained. The pressure may be applied in a different power according to the user or measure time. Therefore, there is a need to provide indices indicating how hard the pressure is applied so as to obtain an enhanced elastic image in the ultrasound system.